A challenging aspect of treating those who have lost one or more limbs is the restoration of function to the remaining limb (residual limb). Such a restoration often means fitting the residual limb with one or more prostheses, or artificial limbs. A difficulty with artificial limbs is that they often do not physically interface well with the prosthetic patient. For instance, most prostheses comprise a cup, or “socket” into which the residual limb, protected by a sheath or “liner,” is inserted and secured. Over the years, the wearing of prosthetics has become more comfortable due to the adoption of prosthetic liners made of synthetic elastomeric and gel materials. Elastomeric liners have the ability to interface between the skin of the wearer and the hard plastic orthotic socket because they have elastic properties and physical consistencies similar to human tissue and can form a vacuum-aided seal between liner and residual limb. As a result, slipping and buckling with ambulation, a problem with earlier liner types, can be reduced. Such liners are indicated in U.S. Pat. Nos. 5,549,709; 6,645,253; 6,761,742; 6,554,868; 6,726,726; 6,926,742 and 6,974,484.
Current gel liner designs available to amputees are generally simple. Many are based upon a single-layer elastomeric sleeve, usually with a slight taper from the open end to a blunted closed end. Because of such simplicity of design, the liners can be manufactured in large numbers from easily worked materials at a relatively low cost.
A problem with elastomerics is their ability to thermally insulate, which tends to increase the rate at which the residual limb perspires. The supple elasticity which makes elastomeric liners suitable for long term skin contact can have negative consequences when the contact with the skin is broken by a liquid, such as perspiration. While mild perspiration may enhance the seal between the residual limb and the liner, the amount produced quickly increases such that a layer of perspiration is formed between the liner surface and the residual limb surface.
Because of the pressures exerted on the liner during ambulation, particularly by the prosthetic socket, the liner can pull away from the residual limb, causing air to be sucked into the liner. As the air pockets join upon further ambulation, a volume is produced between the liner and the limb. The air in the volume contracts and expands with each step, creating a suction and causing the residual limb to expand inside the liner. Such an expansion affects the fit of the limb and liner inside the socket. Many methods for fitting the limb inside the prosthetic socket can require that the limb be repositioned in order to give a comfortable fit. However, upon cessation of ambulation, such as while sitting down or sleeping, it is not uncommon for the residual limb to shrink inside the liner to its original size, necessitating yet another refitting. Thus, it is of paramount importance that air be excluded from the liner. Toward that end, it is thus important that the build-up of perspiration be prevented, and that perspiration be removed as it is being formed, or soon thereafter, from between the liner and the residual limb.
Methods of attaching the liner-covered residual limb into the orthotic socket figure significantly in the sliding caused by perspiration. For example, the use of lanyard type attachments, such as, for example, those used in Mantelmacher et al., U.S. Patent Application Publication No. 2007/0032883, attach and secure the liner at points well above its distal tip. Perspiration, which is emitted over the entire surface of the residual limb, tends to gravitate toward the distal tip of the liner, rather than at points higher in the liner. Thus, while perspiration can cause sliding at any place on the liner/skin interface, sliding is prevalent at the distal tip. In order to surmount the difficulties associated with sliding at the distal tip, lanyard systems or similar methods have been developed which attempt to immobilize the liner through the application of radial and circumferential forces by straps or lanyards at liner points above the distal tip. With lanyard or other methods which apply force at ulterior points of the liner, a residual limb/liner can be effectively immobilized in a prosthetic socket. However, such systems can interfere with the comfort of wearing an elastomeric liner. Furthermore, in the absence of a means for evacuating perspiration from the liner, perspiration can accumulate to such a degree that much of the residual limb/liner interface is affected by perspiration and sliding can occur, despite the presence of the securing means. In such a situation, the securing means can result in chafing or other skin breakdown which can interfere with the ability to continuously wear the liner for long periods of time. Means of perspiration removal which have been used include vacuum ports or nipples to which a vacuum device is permanently or intermittently attached. Such ports are generally located near the distal tip. The ports can limit the ability of some patients to wear a liner for long periods as the nipple can result in constant pressure through the liner on the residual limb at the site of the nipple, which wearers can find to be unbearable over time.
Another means of attaching a liner-covered residual limb to a prosthetic device involves an attachment pin or spike which protrudes from the distal tip of the liner and inserts into a hole in the prosthetic which opens into the socket. The pin is usually supported by a disc or support which is significantly harder and less elastomeric than the liner material. The support can be completely or partially embedded within the distal tip of the liner. It is generally large, even to the point of occupying most of the distal tip. The support is generally large enough to give adequate support to the pin, such that the need for other liner support is minimized. The large support size also spreads the pressure experienced by the distal tip during standing and ambulation over a larger area such that patient discomfort is minimized. The pin generally has ridges or grooves such that it can be releasably held by the prosthetic.
The connection of the elastomeric liner to the prosthetic socket by pin has associated drawbacks, particularly if the pin is the sole means of connection. For instance, upon the distal accumulation of perspiration, the distal tip of the liner can be prone to pulling away from the residual limb, causing sucking and pistoning which can be even worse than that experienced with lanyard methods due to the immobilization of the distal tip of the liner by the pin attachment. In the absence of other means of attachment, the stability of the limb can be compromised.
A prosthetic liner having the stability associated with a distal tip pin, but without the same susceptibility to performance deterioration due to perspiration build up would represent a welcome advance in the art.